hardpan

hardpan, condition of the soil or subsoil in which the soil grains become cemented together by such bonding agents as iron oxide and calcium carbonate, forming a hard, impervious mass. It is disadvantageous to farming, interfering with the circulation of moisture in the soil and with the growth of roots through the soil. When the condition is caused by the filling of the air spaces in the soil with fine particles of clay, the subsoil is called a clay pan. This usually occurs in acid soil.